Abstract

There were three primary aims of this geomorphological assessment of the Pipers River.First, to evaluate hydraulic flow characteristics of the Pipers River at bankfull discharge.These are the conditions under which channel processes are most active, and channelerosion or avulsion can occur. Second, to describe downstream changes in particle shapeand type of stream bed material, and third, to provide a baseline survey that can berepeated in future for quantitative identification of change.Three sites were assessed at representative sections of Pipers River. Site 1 was locatedjust north of Underwood at 250 meters elevation and within a topographically steeplandscape. Site 2 was located at Colgrave road, about 14 km north of site 1 at anelevation of 65 meters. Site three was east of Baxter road, further 8 km north from site 2,c. 11 km south from Pipers Head and at an elevation of c. 40 meters.The river at site 1 (Underwood) was found to be stable, with establishing riparianvegetation, and unlikely to erode. The river at site 2 was found to be unstable, caused bychannel incision and expansion, leading to increased bankfull discharge and capability forerosion. This was exacerbated by large woody debris in the channel, in positions thatcause bank scour. The river at site 3 was found to be unstable, caused by reducedbankfull discharge, and consequent bed aggradation, which has lead to channel avulsion.This was also contributed to by willow infestation of the channel, and stock access to thechannel.There are specific recommendations from this field assessment to improve conditions atsites 2 and 3, including willow removal, riparian fencing, riparian revegetation, andrivercare assessment of the orientation of large woody debris at site 2, and the channelavulsion exit at site 3. It is further recommended that this survey be repeated in future forquantiative evaluation of changer, either after any major works (upstream or on-site), orevery 5 years.